This invention relates to magnetic bubble memories; and in particular, it relates to mechanisms in such memories for stretching magnetic bubbles prior to their detection.
In a magnetic bubble memory, a planar film of magnetic material is provided in which the magnetic bubbles are formed by a magnetic field that is oriented perpendicular to the plane of the film. An insulating layer is disposed over the film of magnetic material; and a plurality of bubble propagate elements, such as a plurality of asymmetric chevrons, are disposed on the insulating layer to define paths beneath which the magnetic bubbles move. Those bubbles move in response to another magnetic field that rotates in the plane of the propagate elements.
In order to read information from the bubble memory, a sensing mechanism is also provided on the insulating layer to detect the presence (or absence) of the magnetic bubbles. This mechanism includes a magnetostrictive sensing element which changes its resistance as a magnetic bubble is propagated beneath the element. However, the resistance changes are quite small; and so the bubbles are stretched before they are passed under the sensing element in order to avoid errors in their detection.
In other words, the magnitude of the resistance change that is induced into the magnetostrictive sensing element is proportional to the size of the bubble which passes underneath that element. Thus, in a bubble memory, a stretching mechanism is conventionally provided between the bubble propagate elements and the magnetostrictive sensing element to increase the size of the bubbles before they are sensed.
One desirable feature of the bubble stretching mechanism is that the amount by which it stretches a bubble for each rotation of the in-plane rotating magnetic field be relatively large. This is because each rotation of that field takes a certain amount of time; so reducing the number of rotations that are required to stretch the bubble to a given length directly increases the speed at which the bubble is sensed.
Another desirable feature of the bubble stretching mechanism is that it occupies a reduced amount of space. This is because by reducing the space which the stretching mechanism occupies, more space is available for additional propagate elements; and thus the total number of bubbles that can be stored in the memory (i.e., the memory storage capacity) is increased.
Accordingly, a primary object of the invention is to provide an improved mechanism for stretching bubbles in a magnetic bubble memory.
Another object of the invention is to provide a mechanism for stretching bubbles with improved speed.
Still another object of the invention is to provide a mechanism for stretching bubbles in a reduced amount of space.